The single transferable vote, commonly abbreviated STV, is a preferential proportional electoral system used in multi-member constituencies in which voters rank candidates and votes can transfer between candidates according to subsequent preferences. International IDEA defines STV as a preferential system in which voters have one vote in a multi-member district, candidates who reach a specified quota are elected, surplus votes from successful candidates can be transferred, and votes from eliminated candidates can also be redistributed until the required number of representatives has been elected.
The word single refers to the elector having one ballot vote even though that vote can transfer between candidates during the count. The word transferable refers to the movement of electoral value when a voter's preferred candidate has either obtained more support than necessary to win or has been eliminated. STV is therefore fundamentally different from a single-member ranked system such as the alternative vote because STV elects several representatives from each district.
The counting process begins with voters ranking candidates, commonly by marking first preference, second preference, third preference and further preferences. A quota is calculated according to the electoral rules, with the Droop quota being a common formula. Candidates who reach the quota are elected. If an elected candidate has votes exceeding the quota, the surplus is transferred according to the applicable transfer rules, allowing voters' later preferences to influence the allocation of remaining seats.
If no candidate reaches the quota after surplus transfers, the lowest placed candidate is eliminated and that candidate's transferable votes are redistributed according to the next available preferences. The process continues through successive counts until all seats are filled. The exact treatment of surpluses can vary, particularly concerning whether all ballots transfer at a common fractional value or whether particular groups of ballots are selected according to a prescribed method. The general principle remains repeated transfer until the required number of candidates reaches the electoral quota.
STV differs fundamentally from list proportional representation because voters normally choose individual candidates rather than simply selecting a party list. Several candidates from the same party can compete within the same multi-member constituency, and voters can rank candidates from different parties in whatever order the rules permit. This creates a candidate-centred form of proportional representation. The system can preserve proportional outcomes while giving voters substantial influence over which individual candidates receive seats.
It also differs from open-list PR because STV does not normally allocate a predetermined number of seats to each party and then determine the successful candidates from a party list. Instead, candidates compete directly in a common preferential count and seats are filled sequentially according to quotas and transfers. Party representation emerges from the aggregate results of individual candidates rather than from a separate party-list allocation stage.
District magnitude is particularly important under STV because the number of representatives elected from each constituency affects the quota required to win. A district electing three members has a substantially higher quota than one electing seven members, meaning that the electoral threshold for representation changes with district magnitude. Larger districts can permit more groups to gain representation because candidates need a smaller proportion of the vote to reach the quota.
Smaller districts produce a higher threshold and can make representation more concentrated. Boundary design therefore interacts directly with the proportional characteristics of STV. Voters may also have many candidates to rank, which can make ballot information and voter education important. The system is consequently not merely a counting method. It combines preferential voting, multi-member districts, a quota, transfer rules and elimination procedures, all of which jointly determine how votes become seats.
The transfer mechanism is central to the meaning of STV. Suppose a candidate receives substantially more first preferences than the quota requires. Those surplus votes are not simply discarded. Under the system's transfer rules, part of their electoral value can pass to voters' later preferences. Likewise, when a candidate with too few votes is eliminated, ballots supporting that candidate can transfer to the next preferred eligible candidate.
This means that voters can influence several stages of the count even though they cast only one ballot. A voter's later preferences may eventually become decisive if the first choice is elected with surplus support or eliminated. The system therefore reduces the extent to which votes become electorally irrelevant after the first preference has failed to determine a result. The precise mathematics of transfers can be complex, particularly when fractional values are involved, but the conceptual principle is straightforward: preferences can continue to influence which candidates fill the remaining seats.
STV also has a distinctive relationship with party politics. Parties can nominate multiple candidates in the same constituency, and voters can rank those candidates relative to candidates from other parties. This creates the possibility of competition between candidates from the same party as well as competition between parties. Candidate reputation, local organisation, personal campaigning and preference transfers can therefore become important.
Parties may provide guidance about preferred rankings, but the electoral system itself gives voters the ability to determine their own ranking. In some implementations, party identification remains highly important because voters use party affiliation as an informational shortcut, while in others individual candidate characteristics play a substantial role. The system therefore combines proportional representation with candidate-centred preferential voting rather than requiring voters to accept a fixed party ordering. International IDEA identifies STV as a candidate-centred preferential system operating in multi-member districts.
STV is used in several jurisdictions and has particularly strong historical associations with Ireland and Malta, while Australia uses STV for its federal Senate and in other electoral contexts with specific variants. International IDEA identifies Ireland and Malta among countries using STV and Australia for its upper house in its comparative classification. Different jurisdictions use different ballot rules, district sizes, quota calculations and transfer procedures, so practical operation is not identical everywhere.
The system can be used for parliamentary, local or other elections and can coexist with different constitutional arrangements. Its use in multi-member constituencies distinguishes it from the alternative vote, even though both use ranked preferences and transferable ballots. This distinction is important because a ranked ballot does not by itself determine whether an election is proportional. The number of seats and the counting method are equally fundamental.
The single transferable vote is therefore a preferential proportional system in which voters rank individual candidates in multi-member districts and their votes can transfer through successive counts until enough candidates reach the required quota to fill all available seats. Its defining components are the multi-member constituency, preferential ballot, quota, election of candidates who reach the quota, transfer of surpluses and transfer of votes from eliminated candidates.
STV should not be confused with the alternative vote, which normally uses one seat per district and transfers preferences until one candidate obtains a majority. It should also not be confused with open-list PR because STV does not normally use a separate party-list seat allocation mechanism. STV instead creates proportional representation through the collective behaviour of individual candidate preferences and transfers.
